Starvation

THE ENDOCRINE SYSTEM

[ANSWER]

Starvation

1. A typical, healthy adult man in the resting basal state expends approximately 20 kcal/kg, which equals 1400 kcal/day in this person.

A 26-year-old male prisoner begins a hunger strike

Ordinary

to protest what he considers unfair prison policies.

account for another 300 to 400 kcal/day. His 1

He drinks only tap water, and his only exercise is

hour of exercise would require approximately

two daily half-hour walks at approximately 2.5

250

miles/hr. The temperature in his cell is maintained

expenditure might be approximately 2000

at 72 oF. His starting weight is 70 kg (154 lbs), of

kcal initially. As fasting continued, his basal

which 14% is body fat. At the end of 4 weeks, he is

metabolic rate would diminish about 15% to

urged by the prison physician, family, friends, and

approximately 1200 kcal/day and lethargy

his attorney to stop his fast because of his

might also reduce both spontaneous and

deteriorating condition.

voluntary physical movement. Thus, for the 4

1. What would you estimate his daily energy expenditure to be? 2. Approximately how much weight would he have lost

in

4

weeks?

What

would

be

the

kcal.

spontaneous

Thus

his

movements

total

daily

would

energy

weeks, his overall energy expenditure could average 1800 kcal/day. 2. His total caloric needs for 28 days would be 56,000 endogenous kcal (1800 per day x 28

approximate distribution of this lost weight in

days).

Ninety

percent

of

this

would

be

carbohydrate, protein, and fat? In lean body

supplied by fat at 9 kcal/g. Thus, 0.9 x 56,000

mass and adipose tissue? What would his

¡Â 9 equals 5600 g or 5.6 kg of fat. Adipose

respiratory quotient be at that time?

tissue is composed of 15% water. Hence, 5.6 ¡Â 0.85 or 6.6 kg of adipose tissue would be

3. What changes in plasma levels of energy

lost. Ten percent of the caloric needs would be

substrates would occur in the first 3 days of

supplied by protein at 4 kcal/g. Thus, 0.1 x

his fast? What changes in urinary constituents

56,000 ¡Â 4 equals 1400 g or 1.4 kg of protein

would be expected?

that would be lost. The source of this protein

4. On what immediate and on what ultimate

is lean body mass, which is composed of 72%

sources of energy would brain metabolism

water. Thus, 1.4 ¡Â 0.28, or 5 kg, of lean body

depend?

mass would be lost. Carbohydrate stores of energy are very low and contribute no more

5. What early changes in plasma levels of hormones

would

occur?

How

would

this

regulate his energy metabolism? 6.

What

other

hormonal

compensatory

mechanisms would be called into play to conserve energy and prolong life?

than 0.3 to 0.4 kg, all in the first 2 days. Thus the estimated total weight loss would be 6.6 plus 5, plus 0.4, or 12 kg. His respiratory quotient would be slightly greater than 0.7 because of the predominance of fat as a substrate for oxidation.

7. What physiologic events would occur when he

3. Plasma glucose would decrease to a lower,

stopped his fast by drinking a large quantity of

but stable level after glycogen stores were

orange juice?

depleted. Plasma free fatty acids and glycerol would

increase

lipolysis,

and

because keto

of

accelerated

acids

(betaPage 1 of 2

hydroxybutyrate

would

The loss of somatomedin's stimulation of

increase as a result of increased free fatty

protein synthesis shunts amino acids away

acid delivery to the liver. Plasma branch chain

from anabolic storage toward conversion to

amino

of

needed glucose. Maintenance of cortisol and

Urinary

elevated growth hormone levels diminishes

indicating

the sensitivity of muscle to insulin and further

acids

increased nitrogen

and

would

proteolysis would

acetoacetate)

increase in

because

muscle.

increase,

degradation of endogenous protein. Excretion

preserves the glucose supply to the brain.

of sodium in the urine would promptly cease in the absence of sodium intake after a small

7. Ingestion of any source of carbohydrate would

fall in extracellular fluid volume. Excretion of

raise plasma glucose and thereby rapidly

the predominantly intracellular electrolytes

stimulate insulin release and inhibit glucagon

(potassium and phosphate) would continue,

and

indicating the loss of protoplasm.

oxidation would increase and thus raise the

growth

hormone

release.

Glucose

respiratory quotient. Storage of glucose as 4. Initially, the brain would be almost entirely dependent

on

glucose

generated

glycogen

in

liver

and

muscle

would

be

by

stimulated by insulin. At the same time,

gluconeogenesis, mostly from amino acid

uptake of potassium and phosphate by these

substrates liberated by muscle proteolysis.

tissues

Gradually, however, keto acids generated by

decrease in their plasma levels. A sharp

oxidation of free fatty acids would become

decrease in plasma free fatty acids, keto

brain substrates and would eventually supply

acids, and branch chain amino acids would be

two thirds of the brain's energy needs. This

expected as the high insulin levels reduced

would help to conserve lean body mass

lipolysis, ketogenesis, and proteolysis.

would

be

stimulated,

causing

a

during fasting. 5. Plasma insulin would decrease and plasma glucagon would increase. The lower ratio of insulin to glucagon facilitates mobilization of liver glycogen, adipose tissue triglycerides, and muscle protein. 6. Serum thyroid-stimulating hormone (TSH) and its response to thyrotropin-releasing hormone (TRH) would decrease. In addition, serum triiodothyronine (T3) would decrease because of reduced 5' monodeiodination of thyroxine (T4). The net result is a lower level of the active T3 molecule, which contributes to the decrease

in

resting

energy

expenditure.

Cortisol secretion would increase modestly, facilitating

muscle

gluconeogenesis. increase, conversion

and

hormone

levels

Growth

facilitating of

proteolysis lipolysis.

growth

However,

hormone

to

somatomedin would be greatly diminished. Page 2 of 2